1. Field of the Invention
The present invention relates to a quick-releasing linear actuator, and in particular to a quick-releasing linear actuator suitable for an electric hospital bed.
2. Description of Prior Art
It is well known that linear actuators can be widely used in electric hospital beds, patient lifters, treadmills, and wheelchairs for adjusting positions. When a patient is subjected to emergent medical treatment or emergency situation like CPR—Cadio Pulmonary Resuscitation, a quick-releasing linear actuator is capable of quick changing and adjusting the position of the hospital bed, so that the most important time for rescuing the patient will not be wasted. Therefore, a linear actuator capable of quick releasing has become an important issue in this art. By An external damper or braking system or by the internal friction of the actuator, the speed or the time to release the actuator can be adjusted depending the demand of the application.
A conventional linear actuator mainly comprises a motor means, a transmission means and a pulling arm means. The motor means comprises a motor and a base connected to the motor. The motor is provided with a worm penetrating into the base. Further, the transmission means has a screw penetrating out of the base, a worm gear connected to one end of the screw and engaged with the worm inside the base, and a telescopic tube threadedly connected to the other end of the screw. The pulling arm means has a pulling arm connected to the worm gear. By pulling the pulling arm to pull out the engaging worm and worm gear, at this time, the screw can coaxially rotate with the worm gear so that an axial force can be exerted to the telescopic tube to make it to retract inwardly, thereby to quick release the hospital bed.
However, when in use, there are still some drawbacks existing in conventional linear actuators. Since the worm gear is positioned within the base and axially movable with respect to the screw, the space necessary for the base is larger, and thus the overall size of the linear actuator is greatly increased. Further, when the motor is out of order, the worm becomes immobile and locked, such that the pulling arm cannot pull out the worm gear along the screw, disenabling to function normally. Moreover, the action in which the pulling arm directly pulls the engaging worm and worm gear needs a lager pulling force, which easily causes a large movement or a large force incompatible with the emergency case like the CPR.
Therefore, in view of the above the drawbacks, the inventor proposes the present invention to overcome the above problems based on his expert experiences and deliberate researches.